[Solved] CS558 Introduction To Computer Security Assignment 2

1. (4 points) which of the following attacks are passive attacks (one or more answers may be correct)?

1. Traffic analysis B. Denial of service C. Replay attack D. Masquerade

2. (12 points) Let Pu_A and Pr_A be Alices public and private keys, respectively, and Pu_B and Pr_B be Bobs public and private keys, respectively. Assume that Alice sends Bob a message M.

1. If Alice wants to protect the confidentiality of M, then what key should Alice use to encrypt M?

1. If Alice wants to provide digital signature, then what key should Alice use to create the digital signature?

1. If Alice wants to protect the data integrity of M, then what key should Alice use to encrypt M?

3. (8 points) Suppose 4 people want to communicate securely with each other such that the communication of none of the possible pairs of people can be eavesdropped by the remaining persons. Answer the following questions:
   1. If they use a symmetric cipher, how many symmetric keys would they need in total?

1. If they use a public-key cipher, how many public and private keys would they need in total?

4. [15 points] Encrypt the message tomorrowfriday using rail fence cipher with depth 4

5. [15 points] Decrypt the message rnoxitrzsunwinooagry using row transposition cipher and key: 35214

6. [7 points] Given the following permutation table (P table)

Assume that the input of the P table is 11000000 00000000 00000000 00000000, which bits of the output of the P table are 1?

7. [15 points] Consider the following S-box. Assume that the output of this S-box is 2, What are the four possible inputs to S-box?

8. [8 points] Compute (55), where is Euler totient function.
9. [16 points] Consider the following simple hash function H, which computes the hash code H(M) of a message consisting of n blocks b1, b2, , bn.

hi = bi1bi2 bin

hi: the ith bit of the hash code bij: the ith bit of the jth block

Assume that the block size is 4-bits and Alice sends message M = 0110 1001 1101 0101 to Bob.

Answer the following two questions:

• (8 points) what is the hash code H(M)?
• (8 points) show that this hash function is not secure by creating another message M so that H(M) = H(M).

Submission guideline

You need to hand in your assignment through mycourses.binghamton.edu, which contains: 1) Your name and email address; and 2) Solution to the problems. Your assignment must be in .pdf format. You can write down the solution in a paper, take a picture of the solution, and then upload the solution.